Method for ceramic work in prosthetic dentistry



Jan. 11, 1966 R. G. BOWMAN 3,229,003

METHOD FOR CERAMIC WORK IN PROSTHETIC DENTISTRY Filed March 15, 1962 Z2 Z 41 3e 39 INVENTOR. ROM-W76? BdA/MA/I/ United States Patent 3,22,003 ETHOD FOR CERAMHC WGRK IN PROSTHETIC DENTISTRY Robert G. Bowman, 1249 Madison Ave., SE, Grand Rapids, Mich. Filed Mar. 15, 19-62, Ser. No. 179,976 4 Ciaims. Ii. 264-19) This invention relates to a method for building ceramic crowns and bridgework, and more particularly to a method for coating a die surface or matrix with a ceramic material, especially for applying dental porcelain to a die surface or matrix on a tooth cast. In the following dcscription and claims, it should be understood that any reference to crowns should be taken to include ceramic bridgework made by the same method.

An important factor in determining the health, wellbeing and appearance of people is the physical condition and appearance of their teeth. Custom-made jacket crowns are an important part of this factor. However, the most skillfully hand-made crowns do not ordinarily possess the most desirable characteristics, both structurally and esthetically, due to limitations in the usual methods of forming this coating. Optimum characteristics of jacket crowns involve (l) strength, (2) durability, and (3) appearance (to closely resemble natural tooth enamel), i.e. good translucency, color, fluorescence, and refraction. To obtain these qualities in desired amounts in the finished product (i.e. after firing), the immature porcelain coating (i.e. before firing) must be both extremely dense and of substantial thickness. With conventional hand-coating methods in which the porcelain is condensed by rubbing a serrated portion (S in FIG. 1 of the drawings) of a tool against the cast, it is practically impossible to obtain optimum amounts of all three qualities because these methods do not permit sufiicient condensation and dehydration of the porcelain. With present methods, the immature porcelain coating must be made thicker than the desired thickness of the finished product to compensate for the rather substantial shrinkage during the firing process. Proper anticipation of the amount of shrinkage and proper compensation for it calls for considerable skill and experience on the part of the laboratory technician. Even then, with conventional methods and apparatus of forming the ceramic coatings of jacket crowns, shrinkage control is so poor that a substantial amount of hand grinding of the finished crown is usually necessary.

Furthermore, an improperly condensed porcelain coating has a tendency to crumble during the forming operation. This is particularly true of a completely ceramic crown (i.e. without gold backing) built up on a platinum matrix.

Most high-quality jacket crowns are composed of several layers of porcelain of varying colors and consistencies which must be applied in varying thicknesses at varying locations on the die or matrix to produce color and translucency gradients in the finished crown that most nearly resemble those of natural teeth. A serious problem in this respect is the necessity of condensing each such layer gradually enough to retain its shape and thickness gradient, yet sufficiently to prevent it from running or spreading uncontrollably when another layer is applied over it. Present methods are very poor in this respect.

Finally, uneven or insufiicient condensation of the porcelain causes the enamel to become milky and brittle upon firing. This condition is not apparent while the porcelain is in its immature state and therefore usually results in loss of a great deal of valuable labor.

The present invention solves all these problems by providing means for applying uniform vibration of control- "Ice lable intensity to the cast and die or matrix. This makes it possible, by repeated vibration and fiuid removal steps, to gradually condense each layer of porcelain to a much firmer and more uniform consistency than was heretofore possible without causing it to run uncontrollably during the condensation process. The resulting increased density and hardness of the immature porcelain makes the unfired jacket much easier to shape, and shrinkage during firing is greatly reduced. In addition, the homogeneity of the porcelain and the precise location of the various layers gives the fired enamel a far better and more natural appearance than was heretofore possible.

It is therefore the primary object of this invention to provide a novel method for forming a ceramic coating or jacket on a crown die surface or matrix so that the finished crown is durable, strong, has unusually fine esthetic qualities, and can be accurately shaped and dimensioned with a minimum of labor.

Another object of the novel method is to enable the immature ceramic coating or jacket to be firm and dense with excellent definition between the layers of the coating without sacrifice of bonding between adjacent layers.

A further object of the invention is to produce a jacket crown which has better light refraction and translucency characteristics than was previously possible, so as to appear extremely natural.

It is still another object of the invention to provide ex.- cellent shrinkage control of the enamel coating upon firing so as to reduce subsequent hand grinding to little or nothing.

These and other objects of this invention will be apparent upon studying the following specification in conjunction with the drawings, in which:

FIG. 1 is a perspective view showing the novel apparatus of this invention, including a vibrator and a tooth cast, and illustrating part of the method of this invention;

FIG. 2 is a perspective enlarged view of the vibrator illustrated in FIG. 1; and

FIG. 3 is a cross-sectional view taken on plane IIIIII of FIG. 2.

Basically, the novel method of making jacket crowns achieves a dense, thick ceramic coating with sharply defined but well bonded layers on a die or matrix, by intermittently applying small quantities of a suspension of ceramic material to the die surface, and subjecting the cast supporting the die or matrix to a mechanical vibration of uniform frequency on the order of sixty cycles per second to precipitate and condense particles of the ceramic material. The carrying fluid which has collected on the surface of the precipitated ceramic material is then removed, whereupon the cast is re-vibrated more intensely than before. The accumulated fluid is then again removed, and the process is repeated with more and more intense vibration until the ceramic material has become dense and hard. The ceramic material is then shaped with a finishing tool and fired, usually in a vacuum, to form the finished enamel. The intermittent application of the suspension followed by several vibration and fluid removal steps is repeated a number of times to obtain the desired thickness and layer arrangement of the jacket crown.

Referring now to the drawings, in FIG. 1 are shown hands 10 and 12 of a technician holding a cast 14. A platinum die 16 to be coated with dental porcelain is inserted into the cast 14. Adjacent cast 14 is a vibrator 18 having an anvil 20 which may have a fiat upper surface (FIGS. 2 and 3), and including hand rest and reference areas 22 adjacent anvil 20. The vibrator 18 as shown in FIGS. 2 and 3 includes a housing, within which are mounted electrical windings 24 adapted to be connected to a conventional electrical outlet (not shown) by electrical leads 26 which pass through an on-off switch 28. In the alternative, a treadle-type remote control switch (not shown) may be substituted for the switch 28. A magnetic core 30 is excited by the windings 24 at the standard power line frequency of sixty cycles per second. Spaced above the upper surface of the core 30 and adjacent thereto, and held securely in position With respect thereto by generally U-shaped rubber mounting means 32, is a flat, planar steel spring element 34 upon which rests the lower surface of cylindrical post 36 of anvil 29. Post 36 is slidably mounted within a bearing sleeve 38 in the housing of the vibrator and includes a peripheral radially outwardly extending lower flange 40. Sleeve 38 also includes a radially outwardly extending flange 39 spaced above flange 40 by a compressible, resilient annular element 42 of rubber or the like.

The top surface of anvil 20 may be made substantially flat but with rounded edges, as best shown in FIG. 3, in order that it may contact a substantial area of cast 14, thereby distributing the vibratory impact forces over this area to prevent splitting of the cast 14 during vibration. The rounded edges of the anvil in this case permit accurate angle control for fine work where splitting of the cast is no problem.

In the alternative, a metal, plastic or other nonbrittle element 41 may be cast into the cast in such a manner that it will absorb the impact of the anvil during the coating process.

The cast may be formed of conventional plaster-type materials or their equivalent, and is adapted to receive therein metallic tooth base or die elements upon which a porcelain coating or jacket is formed.

Method To form a porcelain coating or jacket crown on a die or matrix in accordance with this invention, a cast 14 is formed to receive the die or matrix, e.g. 16, on which the crown is to be built. Then switch 28 of the vibrator is thrown to actuate the vibrator so as to cause anvil 20 to reciprocate at the rate of sixty cycles per second. The uniform frequency of the vibration produces a consistent condensation for a given composition of the porcelain suspension and a given amount of pressure on the cast. Next, a small amount of a suspension of ceramic particles in a fluid such as water in the form of a droplet is placed on the surface of die 16 as by a spatula 17. The suspension may comprise any one of a number of well-known dental porcelains which may be obtained from a variety of suppliers. The lower end of cast 14 is then placed firmly against the anvil 26. At the beginning, the anvil vibrates just slightly since the steel spring 34 is biased to its extreme position away from the core 30. Upon placing his hands on surfaces 22 to obtain reference and support, the technician then pushes the cast against the anvil with a force just sufficient to increase the intensity of the vibration to the desired level. Since the suspension is very fluid at first, the vibration is initially held to a minimum intensity to avoid uncontrolled spreading and deterioration of the ceramic material. The vibration causes the particles of ceramic material to precipitate and causes the fluid in the suspension to collect on the surface of the suspension. Then the cast is removed from the anvil and the fluid collectedon the surface is removed, e.g. by blotting. To obtain a more dense layer, the cast is again placed in contact with anvil 20 and it is now depressed more than the first time to cause a more intense vibration of the cast. It will be understood that as the anvil 20 is depressed greater and greater amounts, its lower surface moves the spring 34 closer and closer to the core 30 to reduce the magneto gap and cause the vibration to become more intense. Thus, the technician or operator can control the intensity of the vibration accurately by pivoting his hands, utilizing surface area 22 as a reference. Since part of the fluid has already been removed from the suspension during the first vibration period, the suspension now assumes more of a self-supporting characteristic. It thus can be subjected to more severe vibration. During the second and more severe vibratory period, additional fluid collects on the surface. It is removed also. The cast may thereupon be subjected to even more severe vibration and the moisture then again removed. These steps of increasingly intense vibration may be repeated as often as is necessary to obtain the desired density of material.

After the first layer of enamel has been condensed to the desired density, additional suspension is applied to the surface. It also is subjected to slight vibration, and then to increasingly severe vibration as described above. A substantial number of the second layer particles thereby become embedded in the first layer to effectively integrate the layers into a bonded coating; yet the first layer is now hard enough so that it will no longer run when the the second layer is applied. The same is true of subsequent layers with respect to their adjacent layers. The number of intermittent applications of suspension droplets and thus the number of layers will be determined by the desired ultimate characteristics of the finished jacket crown. By this method therefore, an extremely dense and homogeneous porcelain coating is obtained which is easily workable and is subject to very little shrinkage upon firing. The layers of the coating are moreover integrated well with each other and closely espouse the matrix or die surface. After the desired shape and thickness is obtained, the ceramic is fired in a conventional manner to form the desired fused substance of the finished jacket crown.

Various modifications of the invention within the teachings set forth will be obvious to those in the art. Therefore, the invention is not to be limited to the illustrative forms depicted but only by the scope of the appended claims and the reasonable equivalents thereto.

I claim:

1. A method of building dense tooth jacket crowns on a die, comprising the steps of: applying a droplet of a ceramic suspension to the surface of said die; subjecting said die to control vibrations of minimum intensity to cause said suspension to spread and precipitate on said surface while simultaneously causing fluid in said suspension to collect on the surface of said suspension; removing said collected fluid; then repeatedly subjecting said die to increasingly severe controlled vibration to compact said suspension further and cause additional fluid to collect on said surface; removing said additional fluid after each vibration period; repeating the above steps until a desired thickness of layers of ceramic suspensions is obtained; and firing said combined layers of ceramic suspension.

2. A method of building dense tooth jacket crowns on a die, comprising the steps of: applying a droplet of a ceramic suspension to the surface of said die; subjecting said die to controlled vibrations of minimum intensity to cause said suspension to precipitate on said surface while simultaneously causing fluid in said suspension to collect on the surface of said suspension; removing said collected fluid; repeatedly subjecting said die to increasingly severe controlled vibration to compact said suspension further and cause additional fluid to collect on said surface; removing said additional fluid after each vibration period; applying more droplets of said ceramic suspension to said die surface; repeating the increasingly severe vibration steps and removing the collected fluid; shaping said ceramic material to its ultimate form immediately following said fluid removal; repeating the above steps until a desired thickness of layers of ceramic suspensions is obtained; and firing said ceramic suspension.

3. A method of forming a dense ceramic dental coating on a surface comprising the steps of: applying a droplet of suspension of ceramic material to said surface; subjecting said surface and suspension to controlled vibration of minimum intensity suflicient to precipitate the ceramic particles of said suspension on said surface to form a mass uniform enough and hard enough to substantially retain its shape upon application of additional suspension thereover followed by additional vibration, while simultaneously causing the suspension fluid to collect on the surface of said particles; removing said fluid; subjecting said surface to increasingly severe controlled vibration to additionally compact said suspension; repeating this process to obtain a coating of a predetermined thickness and composition of suspension particles; and firing said coating.

4. A method of forming a dense ceramic dental coating on a surface comprising the steps of: applying a droplet of suspension of ceramic material to said surface; subjecting said surface and suspension to controlled vibration of minimum intensity to precipitate the ceramic particles of said suspension on said surface while simultaneously causing the suspension fluid to collect on the surface of said suspension; removing said fluid; and intermittently subjecting said surface and suspension to increasingly severe controlled vibrations while removing the collected fluid after each vibration period to steadily condense said precipitate until said precipitate is uniform enough and hard enough to substantially retain its shape and position on said surface upon application of additional suspension thereover followed by additional vibration; repeating the above steps to obtain a coating of desired composition and thickness; and firing said coating.

References Cited by the Examiner UNITED STATES PATENTS 719,244 1/1903 Mooney 264-72 2,181,694 11/1939 Felcher 264-71 2,245,291 6/1941 Myerson 264-19 2,533,263 12/1950 Johnson 264-69 2,744,326 5/1956 Chaiken et al. 32-12 2,799,933 7/1957 Neustadter 32-12 2,857,938 10/1958 Wahl 141-71 2,918,717 12/1959 StruXness et al -156 2,939,199 6/1960 Strivens 25-156 2,984,267 5/1961 Gross 141-71 3,042,594 7/ 1962 Hauth 264-69 ALEXANDER H. BRODMERKEL, Primary Examiner.

RICHARD J. HOFFMAN, Examiner. 

1. A METHOD OF BUILDING DENSE TOOTH JACKET CROWNS ON A DIE, COMPRISIG THE STEPS OF: APPLYING A DROPLET OF A CERAMIC SUSPENSION TO THE SURFACE OF SAID DIE; SUBJECTING SAID DIE TO CONTROL VIBRATIONS OF MINIMUM INTENSITY TO CAUSE SAID SUSPENSION TO SPREAD AND PRECIPITATE ON SAID SURFACE WHILE SIMULTANEOUSLY CAUSING FLUID IN SAID SUSPENSION TO COLLECT ON THE SURFACE OF SAID SUSPENSION; REMOVING SAID COLLECTED FLUID; THEN REPEATEDLY SUBJECTING SAID DIE TO INCREASINGLY SEVERE CONTROLLED VIBRATION TO COMPACT SAID SUSPENSION FURTHER AND CAUSE ADDITIONAL FLUID TO COLLECT ON SAID SURFACE; REMOVING SAID ADDITIONAL FLUID AFTER EACH VIBRATION PERIOD; REPEATING THE ABOVE STEPS UNTIL A DESIRE THICKNESS OF LAYERS OF CERAMIC SUSPENSIONS IS OBTAINED; AND FIRING SAID COMBINED LAYERS OF CERAMIC SUSPENSION. 